If you’re wondering whether or not you can lay tile directly on a plywood subfloor, the answer is no. Why? When the tile is laid on top of a plywood subfloor, the plywood will expand over the years.
As a result, the grout lines and the tiles themselves can crack and become damaged. In addition to this, tile can not properly adhere to wood the way it does to concrete.
Instead of laying tile on a plywood subfloor, it’s better to lay a cement board on top of the plywood subfloor first. However, before you lay your cement board, there’s a little prep work that needs to be completed first.
Necessary prep work
The first thing you’ll want to do is check your plywood subfloor for any bending or deflection. These two issues can cause grout joints to pop or the tile to crack and/or become loose.
You can try and examine the subfloor with your eyes, but sometimes it’s hard to see a bent or deflected subfloor. Instead, lay a glass of water on the subfloor, walk across it, and look and see if the water is moving at all. If not, you know you’re in the clear.
In addition to a flat surface, your subfloor must also be at least 1 ½ inch thick. This is the standard size for tiling. If you add a second layer of plywood, locate the seams where the two sheets meet and offset them from each other. This will add extra strength while also helping prevent flexing.
Making sure your plywood subfloor is properly screwed or nailed is also important. Use a chalk line to create your grid. You’ll want to make sure that your plywood subfloor is screwed or nailed every 6 inches around the outside and every 8 inches everywhere else.
Make sure you use long enough screws or nails to drive through the complete subfloor and make sure all the screw or nail heads are at least flush, if not below the surface.
Lastly, make sure there’s a 1/16th-inch gap present between sheets. This gives them room for expansion. By neglecting to do this, you can cause the sheets to bend or warp. Once you have marked all these preparations off your list, the tiling process can begin.
Laying a cement board under a tile
When using a cement backer board, you can go with whether a ½ inch thickness or a ¼ inch thickness. It depends on how high you want to raise your floor.
After you have decided on the thickness and purchased your cement backer board, spread adhesive on both the plywood subfloor and the one side of the cement board. Use a thin-set adhesive. This works best.
Now that you have spread the adhesive and laid down the cement board screw the cement board down. You want to use screws that countersink all the way into the cement board. Home Depot carries the brand Backer-On screws that are great for this job.
When screwing the cement board down, space them about 16 inches apart. This will ensure your cement board is properly attached to the plywood subfloor underneath it. If you remember, tile will not adhere to wood nearly as well as it will to concrete.
Beside cement boards, you can also use mortar, even though it’s not preferred. Mortar is a paste made up of a mixture of sand, water, and a binder. You spread it on a particular surface, and after it dries, it acts as a concrete surface. Tile tends to bond to the primer-like surface quite well. Plus, it’s inexpensive and easy to use.
If you’re planning on using mortar instead of cement boards, you’ll want to start by spreading your adhesive and then lay fiberglass reinforced paper mats down onto the adhesive.
Use a wide joint knife or putty to press the paper down firmly onto the adhesive. Once the paper is down, mix your mortar and spread it with a putty or wide joint knife. Make sure that your mortar is spread evenly. You can now lay your tile. It’s that easy.
Laying your tile
Like mentioned above, tile bonds with mortar quite well. When you lay each piece, you’ll want to slide the tile slightly forward and back. This distributes the mortar evenly to the backside of the tile while also creating clean joints with absolutely no ridges.
You’ll then want to insert spacers between the tiles and use a tile puck to ensure the tile is level. These little devices can be purchased at most home improvement stores. If the tile puck clicks when going over the tile, it means one of the tiles is too high. Using a rubber mallet can put the raised tile back down. You’re now ready to grout.
It’s best to let the mortar sit for 24 hours before you begin the grouting process. Once dry, remove the spacers, mix your grout until it’s smooth and creamy, and use a sponge rubber float to fill in the gaps between the tiles.
Always hold the sponge rubber float diagonal when spreading the grout. Let your grout dry for about 45 minutes and then use a grout sponge and water to clean off the excess grout. Your tile floor is now complete.